<!DOCTYPE html>
<html>

	<head>
		<meta charset="utf-8" />
		<title>VUE 学习</title>
	</head>

	<body>
		<div id="app">
			<h1> watch侦听器</h1>
			<div id="app-7">
				<h2>虽然computed计算属性很方便，但是有些事性需要watch来实现</h2>			
				<div id="watch-example">
				  <p>
				    Ask a yes/no question:
				    <input v-model="question">
				  </p>
				  <p>{{ answer }}</p>
				</div>
				
			</div>
		</div>

	</body>
	
	<script src="https://cdn.jsdelivr.net/npm/axios@0.12.0/dist/axios.min.js"></script>
	<script src="https://cdn.jsdelivr.net/npm/lodash@4.13.1/lodash.min.js"></script>
	<script src="https://cdn.jsdelivr.net/npm/vue@2.5.16/dist/vue.js"></script>
	

	<script type="text/javascript">
		
		var app7 = new Vue({
			el: '#watch-example',
			data:{
				question:'',
				answer:"I cannot give you an answer until you ask a question!"
			},
			watch:{
				// 如果 `question` 发生改变，这个函数就会运行
				//这里是指跟踪变量 question的值的变化
			    question: function (newQuestion, oldQuestion) {
			      this.answer = 'Waiting for you to stop typing...'
			      this.debouncedGetAnswer()
			    }
			},
			created: function () {
			    // `_.debounce` 是一个通过 Lodash 限制操作频率的函数。
			    // 在这个例子中，我们希望限制访问 yesno.wtf/api 的频率
			    // AJAX 请求直到用户输入完毕才会发出。想要了解更多关于
			    // `_.debounce` 函数 (及其近亲 `_.throttle`) 的知识，
			    // 请参考：https://lodash.com/docs#debounce
			    this.debouncedGetAnswer = _.debounce(this.getAnswer, 500)
			},
			methods: {
			    getAnswer: function () {
			      if (this.question.indexOf('?') === -1) {
			        this.answer = 'Questions usually contain a question mark. ;-)'
			        return
			      }
			      this.answer = 'Thinking...'
			      var vm = this
			      axios.get('https://yesno.wtf/api')
			        .then(function (response) {
			          vm.answer = _.capitalize(response.data.answer)
			        })
			        .catch(function (error) {
			          vm.answer = 'Error! Could not reach the API. ' + error
			        })
			    }
			}
		});
		//在html中直接写 {{allName}},这里的值就会显示在页面上
		app7.allName = "kalce kub";
		
	</script>

</html>